When metaphors go literally beyond their territories: The impact of age on figurative language

As one of the most integrated components of language, the understanding of metaphors has sparked some of the greatest interest and debate with regard to how and where it is sustained by the brain. Traditionally, the right hemisphere was thought to be the locus of metaphor comprehension. However, the recent literature reported in this article suggests that the processing of metaphors is the product of a complex interplay and cooperation between the two hemispheres. In fact, the question of how the aging brain processes metaphors remains unresolved. The present study aims to provide insight into the nature of changes in the processing of metaphors in normal aging. We describe the different patterns of interhemispheric activation in younger and older adults during processing of literal and conventional metaphorical meanings of words. A total of 10 younger adults and 10 older adults were scanned via 3T functional magnetic resonance imaging while performing a semantic judgment task using pairs of words: targets with literal or conventional metaphorical relationships and distractors paired with concrete or abstract words. The metaphorical-literal contrast showed significant increased activity in the superior frontal gyrus bilaterally in both groups and in the inferior frontal gyrus and the posterior cingulate cortex in the older group only. Both groups showed a left lateralization. We concluded that aging is associated with changes in the pattern of neural activity when processing conventional metaphors. The results are analyzed in the light of the recent literature proposing age-related neurofunctional reorganization, namely the HAROLD and PASA phenomena in the context of language processing.